MAYBE We are left with following problem, upon which TcT provides the certificate MAYBE. Strict Trs: { a__f(X, X) -> a__f(a(), b()) , a__f(X1, X2) -> f(X1, X2) , a__b() -> a() , a__b() -> b() , mark(a()) -> a() , mark(b()) -> a__b() , mark(f(X1, X2)) -> a__f(mark(X1), X2) } Obligation: innermost runtime complexity Answer: MAYBE The input cannot be shown compatible Arrrr..